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Before posting, please read https://www.cgsecurity.org/testdisk.pdf

Populated it with 4 physical drives: 3 x 2 terabyte, and 1 x 4 terabyte. Used the built-in OMV tools to configure the file system etc., which was (using the default settings without making a lot of informed choices) the disks having the ext4 file system with a single logical volume (called "Fantasia") with folders to contain different types of data (music, video, documents, PC backups, software installers). The server boots off 32 gig USB key.

Everything working fine. I add an external 4 bay eSATA enclosure, into which I installed another 4 terabyte drive. Got that set up. At the time I didn't know it but I had only installed the physical disk, hadn't, um, 'extended the logical volume'? I think? It wasn't showing ~14 terabytes. So I did something and got the partition "Fantasia" to "extend" to include the new 4 terabyte drive in the external drive enclosure. Only days later I got my hands on another 4 terabyte drive, so I thought I'd insert it as the second disk in the enclosure, but it wasn't working, so I powered down the external enclosure and put the new 4 terabyte drive in the 1st bay and left the original single drive out of the enclosure.

Long story short, for some reason the file system was no longer accessible.

The folder where the mount point is on my boot drive is empty. I don't recall ever looking there for a virtual file system but there's nothing there now. So I recreated the folders manually (hopefully that didn't actually do anything to the data on the physical disks) but they show up empty.

I really don't know what to do at this point: I believe the files are still there, but I don't know if I can just mount the entire logical volume again or if I have to get another blank disk to recover files to or what not.

so I'm a bit wary of doing much more. I honestly think I may only have to fix something in fstab or what not, but I'm nervous about trying to do that and breaking something or reinstating it as a "blank file system" that will get overwritten.

I've tried googling lots of things about ext4 partiions, 'reconnect logical volume', 'recover files from missing lvm2' etc., etc., etc., and I'm not sure which which cases apply and which things I can do non-destructively.

I tried various techniques using vgconfig and vgcfgrestore but I end up with that "0 logical volume(s)..." error from vgconfig -ay

How would I find a tutorial that is effectively:

"Take three disks that comprise a single volume group and are a single logical volume, and just stick it in another computer, and mount it."

All the tutorials I can find talk about recovering RAID or creating the LV from scratch, and all I want to do is "make my system aware" of the data: from what I can tell, the system is aware of the Physical volumes, and I've been able to make it aware of the Volume Group, but it doesn't see the logical volume no matter what I do. Again, I believe the fact that testdisk sees the drives as partition type "none" isn't a problem, as certain that I didn't issue any commands to wipe the drives: they are configured as the Open Media Vault setup configured them from brand new drives... but with data on them of course.